Battery light stays on for the first 10 min of a journey.

[J3JCV]

Just a quick check before I try and diagnose further.

The battery light stays on for roughly the 1st 10 min of the car running, and only if its the first journey of the day or there has been a good 4 / 5 hours since the last run.

I had suspicions of the battery being worn out so replaced that, but this hasn't rectified the issue. I haven't yet put a multimeter (as I have lost mine) across the terminals when the light is on to see what volts are there but will do next time it happens. Got to work and checked it, but the light was off by then and there was 13.8v showing as one would expect.

I just wanted to know if this is something that has happened to other people and what the issue was, alternator wearing out, lose belt, anything really??

Thanks in advance!

[J3JCV]

Thanks;

Its a 2008 car, so not new but not that old I guess.

So when I started it this evening the light came on and so i measured the voltage at the battery terminals and it was a constant 12.3V, so I drove for a bit and this time after about 5 min the light when out and when I stopped about 15 min later and measured the voltage it was at the expected 13.9V. Car was stationary for 1.5 hrs and then when I started it again the light stayed off the rest of the way home.

It seems to need to warm up or something - very odd.

Unless it's not odd and this is the warning signs of an alternator or voltage regulator packing up - I just don't understand how that happens though?

[J3JCV]

t400ble said:

What car is it?

Ah - good point. A mazda5 2.0l petrol Sport.

[J3JCV]

Thanks - will try that when I get a chance, but you have to take the wheel off, a panel in the wheel arch and then the AC drive belt before changing it (which I was going to do next). Unless the belt tensioner can be slacked off enough to pop it off? I have never used one of those on an engine before as all other cars / boats have relied on the alternator creating the tension.

[J3JCV]

The light doesn’t go off if you give it a lot of revs, but when it gets close to going off properly (after around 7min) it occasionally can be intermittent when you are say pulling away in a low gear.

This morning I rolled it down a gentle slope in 5th with the ignition on, turned it over a few times without starting and the light was on solidly, no flicker at all. It has never changed brightness if that makes any difference as well?

[J3JCV]

I’m going to have to take the tray off the bottom and get underneath to make sure are the connections are perfect - I think it must be heat related expansion making the earth connection good - or something like that!

[J3JCV]

GreenV8S said:

Does this car have a fusible link? I've known those to fail mechanically leaving a dry joint.

No idea - would that make it work intermittently or not at all?

[J3JCV]

Mignon said:

Possibly something eventually gets jiggled into contact again after the car has been moving for a while.

Only thing about this is that it appears to be so regular and down to time between journeys etc think its 4 hours max and the light comes back on.

Its driving me nuts now!

[J3JCV]

JMJ111 said:

Hi. Im late to this thread. I have exactly the same problem. Did you find out what it was? Is it an easy fix?

Hi, changed the alternator in the end. I cant quite remember how I got to that, but been perfect ever since.